sidekick

sidekick (plural sidekicks)

1. (informal) An assistant to another person, especially to a superior or more important person.
   • 2012 May 24, Nathan Rabin, “Film: Reviews: Men In Black 3”, in The Onion AV Club‎:

     In the abstract, Stuhlbarg’s twinkly-eyed sidekick suggests Joe Pesci in Lethal Weapon 2 by way of late-period Robin Williams with an alien twist, but Stuhlbarg makes a character that easily could have come across as precious into a surprisingly palatable, even charming man.

• mentor

• acolyte
• pupil
• wingman